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| United States Patent |
5,293,248
|
|
Bergen
, et al.
|
March 8, 1994
|
System and apparatus for recording and reproducing and extended
definition video signal in/from a track on a magnetic carrier
Abstract
A system for recording and reproducing an extended definition (ED) video
signal in/from a track on a magnetic record carrier wherein an ED video
signal, such as a PAL-PLUS video signal, includes first lines having a
first luminance signal (Y.sub.1) and a chrominance signal (C), and second
lines having no chrominance signal but a second luminance signal (Y.sub.2)
in the form of a modulated luminance signal with suppressed carrier. The
recording device includes a first signal path (11,31,32,16) for processing
the first luminance signal, a second signal path (11,18) for processing
the chrominance signal and a third signal path (10,30,32,16) for
processing the second luminance signal prior to the three signals being
combined (22) and recorded on the record carrier. The reproducing device
also includes a first (48,50) a second (52,53) and a third signal path
(48,73,83) for processing the first luminance signal, the chrominance
signal, and the second luminance signal, respectively. Furthermore, a
converter is described with which an ED video signal may be converted to a
signal that may be recorded by a video recorder and with which a signal
read out by a video recorder may be converted to an ED video signal.
| Inventors:
|
Bergen; Franciscus H. M. (Eindhoven, NL);
Rotte; Jan J. (Eindhoven, NL);
Nijssen; Stephanus J. J. (Eindhoven, NL);
De With; Peter H. N. (Eindhoven, NL)
|
| Assignee:
|
U.S. Philips Corporation (New York, NY)
|
| Appl. No.:
|
869290 |
| Filed:
|
April 15, 1992 |
Foreign Application Priority Data
| May 06, 1991[EP] | 91201070.9 |
| Feb 27, 1992[EP] | 92200566.5 |
| Current U.S. Class: |
386/37; 386/86 |
| Intern'l Class: |
H04N 009/79 |
| Field of Search: |
358/310,330,11,12,140,141
|
References Cited
U.S. Patent Documents
| 4677497 | Jun., 1987 | Yoshinaka | 358/327.
|
| 4812920 | Mar., 1989 | Nagashima et al. | 358/330.
|
| 4941055 | Jul., 1990 | Fujimoto | 358/330.
|
| 5119208 | Jun., 1992 | Fujimoto | 358/310.
|
Primary Examiner: Chin; Tommy P.
Assistant Examiner: Tran; Thai
Attorney, Agent or Firm: Goodman; Edward W.
Claims
We claim:
1. System for recording and reproducing an extended definition (ED) video
signal in/from a track on a magnetic record carrier, said ED video signal
being in the form of pictures, each picture comprising first lines having
a chrominance signal and a first luminance signal, and second lines
comprising a second luminance signal modulated with a suppressed carrier,
said system comprising a recording device which includes:
an input terminal for receiving the ED video signal;
a separation unit having an input coupled to the input terminal, and first
and second outputs, said separation unit being arranged for deriving the
first luminance signal from the ED video signal and presenting this first
luminance signal at the first output, and for deriving the chrominance
signal and presenting the chrominance signal at the second output;
a first signal path comprising an FM modulator having an input coupled to
said first output of said separation unit, said FM modulator shifting a
frequency range of the first luminance signal to a predetermined frequency
range;
a second signal path comprising a mixer stage having an input coupled to
the other one of said first and second outputs of said separation unit,
said mixer stage mixing the chrominance signal with a predetermined
frequency signal;
a signal combining unit having first and second inputs coupled to an output
of the respective first and second signal paths, and an output for
combining the frequency-shifted first luminance signal and the mixed
chrominance signal; and
writing means having an input coupled to the output of the signal combining
unit for writing the output of the signal combining unit into tracks on
the magnetic record carrier; the system further comprising a reproducing
device which includes:
reading means for reading the video signal written by said writing means
from the tracks on the magnetic record carrier, said reading means having
an output;
a separation unit having an input coupled to the output of the reading
means, first and second outputs, said separation unit being arranged for
deriving the frequency-shifted first luminance signal from the video
signal read from the track by the reading means and presenting this
frequency-shifted first luminance signal at the first output, and for
deriving the mixed chrominance signal and presenting the mixed chrominance
signal at the second output;
a first signal path, including an AM demodulator, having an input coupled
to the first output of said separation unit, said AM demodulator reversing
the effect of the FM modulator on the first luminance signal in the first
signal path in the recording device;
a second signal path, including a mixer stage, having an input coupled to
the second output of said separation unit, said mixer stage restoring the
mixed chrominance signal to that before being applied to the mixer stage
in the second signal path in the recording device;
a first output terminal coupled to an output of the first signal path, for
presenting the first luminance signal; and
a second output terminal coupled to an output of the second signal path,
for applying the restored chrominance signal; characterized in that the
recording device therein further comprises a third signal path having an
output coupled to a third input of the signal combining unit, and
comprises supply means having an input coupled to the input terminal and
an output coupled to an input of the third signal path, said supply means
being arranged for supplying the second luminance signal in the second
lines to the input of the third signal path, in that the reproducing
device therein comprises a third signal path having an input also coupled
to one of the first and second outputs of the separation unit, and an
output coupled to a third output terminal for supplying the second
luminance signal, in that a system signal path leading from the input
terminal of the recording device to the third output terminal of the
reproducing device via the third signal paths in the recording and
reproducing devices comprises at least a first mixer stage, and in that
this first mixer stage is arranged for shifting the frequency spectrum of
the second luminance signal.
2. System as claimed in claim 1, characterized in that the system signal
path comprises a second mixer stage to compensate for frequency inversion
of the second luminance signal caused by said first mixer stage, and in
that at least one of said first and second mixer stages is located in the
third signal path in the reproducing device.
3. A recording device for use in a system for recording and reproducing an
extended definition (ED) video signal in/from a track on a magnetic record
carrier, said ED video signal being in the form of pictures, each picture
comprising first lines having a chrominance signal and a first luminance
signal, and second lines comprising a second luminance signal modulated
with a suppressed carrier, said recording device comprising:
an input terminal for receiving the ED video signal;
a separation unit having an input coupled to the input terminal, and first
and second outputs, said separation unit being arranged for deriving the
first luminance signal from the ED video signal and presenting this first
luminance signal at the first output, and for deriving the chrominance
signal and presenting the chrominance signal at the second output;
a first signal path comprising an FM modulator having an input coupled to
said first output of said separation unit, said FM modulator shifting a
frequency range of the first luminance signal to a predetermined frequency
range;
a second signal path comprising a mixer stage having an input coupled to
the second output of said separation unit, said mixer stage mixing the
chrominance signal with a predetermined frequency signal;
a signal combining unit having first and second inputs coupled to an output
of the respective first and second signal paths, and an output, said
signal combining unit combining the frequency-shifted first luminance
signal and the mixed chrominance signal; and
writing means having an input coupled to the output of the signal combining
unit for writing the output of the signal combining unit into tracks on
the magnetic record carrier; characterized in that the recording device
further comprises:
a third signal path having an output coupled to a third input of the signal
combining unit; and
supply means having an input coupled to the input terminal and an output
coupled to an input of the third signal path, said supply means being
arranged for supplying the second luminance signal in the second lines to
the input of the third signal path.
4. Recording device as claimed in claim 3, characterized in that the third
signal path comprises an FM modulator, said FM modulator shifting a
frequency range of the second luminance signal to a predetermined
frequency range.
5. Recording device as claimed in claim 4, characterized in that the FM
modulator in the first and third signal paths is the same FM modulator
which is shared by the first and third signal paths.
6. Recording device as claimed in claim 3, characterized in that the third
signal path further comprises a first mixer stage arranged for shifting
the frequency spectrum of the second luminance signal.
7. Recording device as claimed in claim 6, characterized in that the mixer
stage in the second signal path and the first mixer stage in the third
signal path is the same mixer stage shared by the second and third signal
paths.
8. Recording device as claimed in claim 5, characterized in that the supply
means comprises first controllable switching means having first and second
inputs coupled to the input terminal and the first output of the
separation unit, respectively, and an output coupled to the input of the
first signal path, the first controllable switching means being arranged
for connecting, in response to a control signal, the first input to the
output at least during the presence of the second luminance signal in the
second lines in the ED video signal, and for connecting the second input
to the output at least during the presence of the first luminance signal
present in the first lines in the ED video signal.
9. Recording device as claimed in claim 8, characterized in that the second
lines in the ED video signal furthermore comprise a burst, in that the
recording device comprises second switching means having an input coupled
to the second output of the separation unit and an output coupled to the
input of the second signal path, and in that the second switching means
are arranged for connecting, in response to the control signal, the input
to the output during the first lines and during the presence of the burst
in the second lines in the ED video signal, and for interrupting the
connection between the input and output during the presence of the second
luminance signal in the second lines.
10. Recording device as claimed in claim 8, characterized in that the
recording device comprises second controllable switching means having
first and second inputs and an output, the output of the first switching
means being coupled to the first input of the second switching means and
an input of the first mixer stage, an output of the first mixer stage
being coupled to the second input of the second switching means, the
output of the second switching means being coupled to the input of the FM
modulator, and the second controllable switching means being arranged for
connecting, in response to the control signal, the second input to the
output at least during the presence of the second luminance signal in the
second lines in the ED video signal, and for connecting the first input to
the output at least during the presence of the first luminance signal in
the first lines.
11. Recording device as claimed in claim 7, characterized in that the
supply means comprises first switching means having first and second
inputs coupled to the input terminal and second output of the separation
unit, respectively, and an output coupled to the input of the mixer stage
in the second signal path, and the recording device further comprising
second switching means having first and second inputs coupled to the first
output of the separation unit and the output of the mixer stage,
respectively, and an output coupled to the input of the FM modulator in
the first signal path, the first switching means being arranged for
connecting, in response to a control signal, the first input to the output
at least during the presence of the second luminance signal in the second
lines in the ED video signal, and for connecting the second input to the
output at least during the presence of the chrominance signal in the first
lines in the ED video signal, and the second switching means being
arranged for connecting, in response to the control signal, the second
input to the output at least during the presence of the second luminance
signal in the second lines, and for connecting the first input to the
output at least during the presence of the first luminance signal in the
first lines.
12. Recording device as claimed in claim 11, characterized in that said
recording device further comprises third controllable switching means
inserted between the output of the mixer stage and the second input of the
signal combining unit, and the third switching means being arranged for
interrupting, in response to the control signal, a connection between the
output of the mixer stage and the second input of the signal combining
unit during the presence of the second luminance signal in the second
lines in the video signal.
13. Recording device as claimed in claim 6, in which the mixer stage in the
second signal path and the first mixer stage in the third signal path is
the same mixer stage shared by the two signal paths, characterized in that
the supply means comprise first controllable switching means having first
and second inputs coupled to the input terminal and the second output of
the separation unit, respectively, and an output coupled to the input of
the mixer stage in the second signal path, and the first switching means
being arranged for connecting, in response to a control signal, the first
input to the output at least during the presence of the second luminance
signal in the second lines in the ED video signal, and for connecting the
second input to the output at least during the presence of the chrominance
signal present in the first lines in this signal.
14. Recording device as claimed in claim 13, in which a low-pass filter is
inserted in the second signal path between the mixer stage and the second
input of the signal combining unit, characterized in that the recording
device further includes switching means for switching off, in response to
the control signal, the filter operation in the low-pass filter at least
during the presence of the second luminance signal in the second lines in
the ED video signal.
15. Reproducing device for use in a system for recording and reproducing an
extended definition (ED) video signal in/from a track on a magnetic record
carrier, said ED video signal being in the form of pictures, each picture
comprising first lines having aa chrominance signal and a first luminance
signal, and second lines comprising a second luminance signal modulated
with a suppressed carrier, said reproducing device comprising:
reading means for reading the video signal written by said writing means
from the tracks on the magnetic record carrier, said reading means having
an output;
a separation unit having an input coupled to the output of the reading
means, first and second outputs, said separation unit being arranged for
deriving a frequency-shifted first luminance signal from the video signal
read from the track by the reading means and presenting this
frequency-shifted first luminance signal at the first output, and for
deriving a mixed chrominance signal and presenting the mixed chrominance
signal at the second output;
a first signal path, including an AM demodulator, having an input coupled
to the first output of said separation unit, said AM demodulator
performing a frequency shift operation thereby restoring the first
luminance signal;
a second signal path, including a mixer stage, having an input coupled to
the second output of said separation unit, said mixer stage performing a
mixing operation with a predetermined frequency signal thereby restoring
the chrominance signal;
a first output terminal coupled to an output of the first signal path, for
presenting the first luminance signal; and
a second output terminal coupled to an output of the second signal path,
for supplying the restored chrominance signal; characterized in that the
reproducing device further comprises:
a third signal path having an input coupled to one of the first and second
outputs of the separation unit and an output coupled to a third output
terminal for supplying the second luminance signal.
16. Reproducing device as claimed in claim 15, characterized in that the
third signal path comprises an FM demodulator.
17. Reproducing device as claimed in claim 16, characterized in that the FM
demodulator in the first and third signal paths is the same FM demodulator
shared by the first and third signal paths.
18. Reproducing device as claimed in claim 16, characterized in that the
third signal path further comprises a first mixer stage arranged for
shifting the frequency spectrum of the second luminance signal.
19. Reproducing device as claimed in claim 18, characterized in that the
mixer stage in the second signal path and the first mixer stage in the
third signal path are the same mixer stage shared by the two signal paths.
20. Reproducing device as claimed in claim 18, characterized in that an
output of the FM demodulator is coupled to an input of the first mixer
stage in the third signal path, an output of which being coupled to the
third output terminal for presenting the second luminance signal modulated
with a suppressed carrier.
21. Reproducing device as claimed in claim 20, characterized in that for
correcting the frequency of the suppressed carrier of the second luminance
signal, the output of the first mixer stage in the third signal path is
coupled to a first input of a phase comparator, an output of which being
coupled through a low-pass filter to a control signal input of a
voltage-controlled oscillator whose output is coupled to a first input of
a third mixer stage, an output of the third mixer stage being coupled to a
second input of the first mixer stage in the third signal path, an output
of a fixed oscillator being coupled to a second input of both the phase
comparator and the third mixer stage.
22. Reproducing device as claimed in claim 21, characterized in that the
output of the first mixer stage is coupled to a first input of a second
mixer stage in the third signal path, an output of which being coupled
both to the third output terminal and to the first input of the phase
comparator, and in that the output of the fixed oscillator is coupled
through a frequency multiplier to a second input of the second mixer
stage.
23. Reproducing device as claimed in claim 21, characterized in that the
first mixer stage in the third signal path and the mixer stage in the
second signal path are the same mixer stage, in that the device further
includes first controllable switching means having first and second inputs
coupled to the output of the FM demodulator and the second output of said
separation unit, respectively, and an output coupled to the input of the
same mixer stage, and in that the first switching means are arranged for
connecting, in response to the control signal, the first input to the
output at least during the presence of the second luminance signal in the
second lines in the ED video signal.
24. Reproducing device as claimed in claim 19, said mixer stage being the
first mixer stage in the third signal path, characterized in that the
separation unit comprises a low-pass filter coupled between the input and
the second output, and in that the separation unit further includes means
for switching off, in response to a control signal, the filter operation
in the low-pass filter at least during the presence of the second
luminance signal in the second lines in the input signal of the separation
unit (FIG. 10).
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a system for recording and reproducing a standard
definition (SD) video signal in/from a track on a magnetic record carrier,
comprising a recording device which includes:
an input terminal for receiving the SD video signal,
a separation unit having an input coupled to the input terminal, and first
and second outputs, which separation unit is arranged for deriving a
luminance signal from the SD video signal and presenting this luminance
signal at the first output, and for deriving a chrominance signal and
presenting same at the second output,
a first signal path comprising an FM modulator,
a second signal path, comprising a mixer stage,
a signal combining unit having first and second inputs coupled to an output
of the respective first and second signal paths, and an output,
writing means having an input coupled to the output of the signal combining
unit, the system further including a reproducing device which comprises
reading means having an output,
a separation unit having an input coupled to the output of the reading
means, first and second outputs, which separation unit is arranged for
deriving an FM-modulated luminance signal from the signal read from the
track by the reading means and presenting this luminance signal at the
first output, and deriving a frequency-converted chrominance signal and
presenting same at the second output,
a first signal path including an FM demodulator,
a second signal path including a mixer stage,
a first output terminal coupled to an output of the first signal path, for
presenting the demodulated luminance signal, and
a second output terminal coupled to an output of the second signal path,
for applying the frequency-shifted chrominance signal, to a recording
device and a reproducing device to be used in the system, to a converter
means for converting a PAL-PLUS video signal to a video signal that can be
recorded on a video tape recorder, and to a converter means for converting
a video signal reproduced by a video tape recorder to a PAL-PLUS video
signal.
2. Description of the Related Art
The system of the type mentioned in the opening paragraph is known, for
example, from Funkschau, No. 6, 1988, pp. 34 and 35. This publication
describes how an SD video signal in the form of a PAL video signal is
recorded on the record carrier by means of a VHS video tape recorder and
an SVHS video tape recorder. Several years ago it was proposed to realize
video pictures having a 16:9 aspect ratio in lieu of video pictures having
a 4:3 aspect ratio. Pictures having such a 16:9 aspect ratio form a better
link to the world of films and to the properties of the human eye. As long
as television sets with 4:3 format picture screens are still used, a
television broadcast in the 16:9 format will have to be
reverse-compatible. Put in other words: for television signals broadcast
in the 16:9 format it must also be possible to be reproduced by a
television set having a 4:3 picture screen. Such a reverse compatibility
can be realized with an extended definition video signal in the form of
the PAL-PLUS television signal. For a description of the PAL-PLUS
television signal, reference be made to two publications in Funkschau, No.
15, 1990, pp. 49-51 and No. 23, 1990, pp. 46-47 and Fernseh- und
Kino-Technik, No. 8, 1989, pp. 407-410 and No. 10, 1989, pp. 522-526.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a system with which recording
and reproducing an extended definition (ED) video signal is possible. The
system according to the invention is thereto characterized, in that the
system is arranged for recording an ED video signal in the form of
pictures, each picture comprising first lines having a chrominance signal
and a first luminance signal and second lines comprising a second
luminance signal modulated with a suppressed carrier, in that the system
is arranged for reproducing the recorded ED video signal, in that the
recording device thereto comprises a third signal path having an output
coupled to a third input of the signal combining unit and comprises supply
means having an input coupled to the input terminal and an output coupled
to the input of the third signal path, which supply means are arranged for
supplying the second luminance signal in the second lines to the input of
the third signal path, in that the reproducing device thereto comprises a
third signal path having an output coupled to a third output terminal for
supplying the second luminance signal, in that the signal path leading
from the input terminal of the recording device to the third output
terminal of the reproducing device via the third signal paths in these
devices comprises at least a first mixer stage, and in that this mixer
stage is arranged for shifting the frequency spectrum of the second
luminance signal.
In a further embodiment the signal path comprises two mixer stages. In that
case the reproducing device always comprises at least one mixer stage.
The invention is based on the understanding that the second lines in the ED
video signal have different contents from the first lines. The second
lines do not have a chrominance signal and, in addition, the second
luminance signal in the second lines is different from the first luminance
signal in the way that the second luminance signal slightly looks like a
chrominance signal as regards its frequency characteristic. The second
luminance signal may be AM or quadrature modulated. According to the
invention the recording device comprises a third signal path for
processing the second luminance signal before this second luminance signal
is combined with the first luminance signal and chrominance signal
processed in the first and second signal paths, after which the combined
signals may be recorded. The reproducing device also comprises a third
signal path for processing the second luminance signal read from the
record carrier.
According to the invention there are now a plurality of options for
processing the second luminance signal in the recording device. Three
options will be further discussed hereinbelow.
In a first option the second luminance signal is subjected to direct FM
modulation in the manner in which the first luminance signal is processed.
There is then a possibility of using the FM modulator in the first signal
path also for FM modulation of the second luminance signal. If the second
luminance signal is not mixed during recording, at least the one mixer
stage (both mixer stages) necessary for further processing the second
luminance signal is (are) located in the third signal path of the
reproducing device. If the third signal path of the reproducing device
comprises not more than one mixer stage, the second luminance signal is
modulated to the baseband by this mixer stage and may then be applied to a
television set as a baseband signal. If the third signal path of the
reproducing device comprises two mixer stages, the original frequency
characteristic of the second luminance signal may be regenerated.
In a second option the second luminance signal is first mixed with a
certain frequency after which the second luminance signal mixed to another
frequency range is FM modulated in an FM modulator. The mixer stage
necessary for this purpose in the third signal path of the recording
device could then be used in common with a mixer stage in the second
signal path. It should be observed here that a second mixer stage is not
necessary per force at the reproducing end. If the mixing frequency has
been properly selected at the recording end, it is possible to regain at
the reproducing end a baseband-demodulated second luminance signal that
can be applied to a television set. If the third signal path of the
reproducing device also comprises a mixer stage, the original frequency
characteristic of the second luminance signal may be regenerated.
In a third option the second luminance signal is also mixed with a certain
frequency and, subsequently, the second luminance signal mixed to another
frequency range is recorded directly via the chrominance channel.
A recording device according to the first and second options may thereto be
characterized, in that the supply means comprise first controllable
switching means having first and second inputs coupled to the input
terminal and the first output of the separation unit respectively, and an
output coupled to the input of the first signal path, and in that the
first switching means are arranged for connecting, in response to a
control signal, the first input to the output at least during the presence
of the second luminance signal in the second lines in the ED video signal,
and for connecting the second input to the output at least during the
presence of the first luminance signal present in the first lines in the
ED video signal.
A recording device according to the first option may further be
characterized, in that the second lines in the ED video signal furthermore
comprise a burst, in that the device comprises second switching means
having an input coupled to the second output of the separation unit and an
output coupled to the input of the second signal path, and in that the
second switching means are arranged for connecting, in response to the
control signal, the input to the output during the first lines and during
the presence of the burst in the second lines in the ED video signal, and
for interrupting the connection between the input and output during the
presence of the second luminance signal in the second lines. This device
subsequently processes the second luminance signal as the first luminance
signal.
In the second option the recording device may be characterized, in that the
device comprises second controllable switching means having first and
second inputs and an output, in that the output of the first switching
means is coupled to the first input of the second switching means and an
input of the first mixer stage, in that an output of the first mixer stage
is coupled to the second input of the second switching means, the output
of the second switching means being coupled to the input of the FM
modulator, in that the second switching means are arranged for connecting,
in response to the control signal, the second input to the output at least
during the presence of the second luminance signal in the second lines in
the ED video signal, and for connecting the first input to the output at
least during the presence of the first luminance signal in the first
lines. In this embodiment the second luminance signal may be mixed with
another frequency than the mixing frequency with which the chrominance
signal is mixed in the mixer stage in the second signal path.
However, the recording device may also be characterized, in that the supply
means comprise first switching means having first and second inputs
coupled to the input terminal and second output of the separation unit
respectively, and an output coupled to the input of the mixer stage in the
second signal path, in that the device further includes second switching
means having first and second inputs coupled to the first output of the
separation unit and the output of the mixer stage, respectively, and an
output coupled to the input of the FM modulator in the first signal path,
in that the first switching means are arranged for connecting, in response
to a control signal, the first input to the output at least during the
presence of the second luminance signal in the second lines in the ED
video signal, and for connecting the second input to the output at least
during the presence of the chrominance signal in the first lines in the ED
video signal, and in that the second switching means are arranged for
connecting, in response to the control signal, the second input to the
output at least during the presence of the second luminance signal in the
second lines, and for connecting the first input to the output at least
during the presence of the first luminance signal in the first lines. In
this case, it will thus be sufficient to have a single mixer stage, that
is to say, the mixer stage in the second signal path which is then used in
common by the second and third signal paths. The mixing frequencies with
which the second luminance signal and the chrominance signal are mixed may
be identical or different.
This recording device may further be characterized, in that third
controllable switching means are inserted between the output of the mixer
stage and the second input of the signal combining unit, and in that the
third switching means are arranged for interrupting, in response to the
control signal, a connection between the output of the mixer stage and the
second input of the signal combining unit during the presence of the
second luminance signal in the second lines in the video signal. This
structure avoids supplying a mixed second luminance signal to the second
input of the signal combining unit during the second lines.
In the third option, the recording device comprising a common mixer stage
for the second and third signal paths may be characterized, in that the
supply means comprise first controllable switching means having first and
second inputs coupled to the input terminal and the second output of the
separation unit, respectively, and an output coupled to the input of the
mixer stage in the second signal path, and in that the first switching
means are arranged for connecting, in response to the control signal, the
first input to the output at least during the presence of the second
luminance signal in the second lines in the ED video signal, and for
connecting the second input to the output at least during the presence of
the chrominance signal present in the first lines in this signal. This
device may further be characterized, in that a low-pass filter is inserted
in the second signal path between the mixer stage and the second input of
the signal combining unit, and in that the device further includes
switching means for switching off, in response to the control signal, the
filter operation in a low-pass filter at least during the presence of the
second luminance signal in the second lines in the ED video signal.
For reproducing the second luminance signal recorded in the first or second
option, the reproducing device is first to demodulate the second luminance
signal in an FM demodulator which may be used in common with the FM
demodulator in the first signal path. A second luminance signal will then
be obtained which is modulated at an unsteady carrier frequency. This is
caused by the time errors occurring while the signal is being read out
from the record carrier. For obtaining a second luminance signal having a
fixed suppressed carrier, the second luminance signal is first still to be
mixed in a manner known per se for the reproduction of a chrominance
signal. Various embodiments of such a reproducing device are described in
the claims 20 to 23. The dependent claim 24 describes a reproducing device
for reading the second luminance signal as recorded with a recording
device of the third option.
The invention furthermore relates to converter means in which an ED video
signal can be converted to a signal that may be recorded by a standard
video recorder, such as a VHS or SVHS video recorder, or a digital video
recorder.
The invention further relates to converter means in which a video signal
reproduced by a standard video recorder, such as a VHS or SVHS video
recorder or a digital video recorder is converted to an ED video signal.
Finally, the invention relates to a record carrier on which the Ed video
signal is recorded.
BRIEF DESCRIPTION OF DRAWINGS
The invention will be further explained in the description of the drawings
following hereinbelow with reference to a number of embodiments. In the
description of the drawings the invention will be described with respect
to the recording and reproduction of a PAL-PLUS video signal. It should be
observed, however, that the invention is likewise applicable to the
recording and reproduction of ED video signals according to a different
standard, such as NTSC, provided that the ED-NTSC signal has the format
specified in this invention. For a description of ED video signals of the
NTSC type, reference be made to EP 357,144 corresponding to U.S. Pat. No.
4,984,078. In the drawings:
FIG. 1 shows a picture as it may be reproduced on a television screen;
FIG. 2a1 shows the frequency spectrum of the first lines of the video
picture while FIG. 2a2 shows the signal content in the first lines of the
video picture, FIG. 2b1 shows the frequency spectrum of the second lines
of the video picture while FIG. 2b2 shows the signal content in the second
lines of the video picture, FIG. 2c shows the frequency spectrum of the
normal PAL video signal as recorded on a record carrier, and FIG. 2d shows
the frequency spectrum of the second luminance signal as recorded in a
wide band on the record carrier;
FIG. 3 shows a first exemplary embodiment of the recording device,
FIG. 4 shows a first exemplary embodiment of a dedicated reproducing
device;
FIG. 5 shows a second exemplary embodiment of a recording device;
FIG. 6 shows a second exemplary embodiment of the reproducing device;
FIG. 7 shows a third exemplary embodiment of a recording device;
FIG. 8 shows a third exemplary embodiment of a reproducing device;
FIG. 9 shows a fourth exemplary embodiment of a recording device;
FIG. 10 shows a fourth exemplary embodiment of a reproducing device;
FIGS. 11 and 13 show the converter means for converting a PAL-PLUS video
signal to a signal suitable for recording by an (S)VHS video tape
recorder;
FIGS. 12, 14 and 15 show the converter means for converting a signal
reproduced by an (S)VHS video tape recorder to a PAL-PLUS video signal;
FIG. 16 shows a block diagram of a digital video recorder;
FIGS. 17 and 20 show the converter means for converting a PAL-PLUS video
signal to a signal suitable for recording by a digital video recorder;
FIGS. 18 and 21 show the converter means for converting a signal reproduced
by a digital video recorder to a PAL-PLUS video signal; and
FIG. 19 shows the second luminance signal with a DC voltage V.sub.DC added.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a picture screen for displaying pictures which have a 4:3
aspect ratio and which are made up of 625 video lines. The 625 lines are
divided over two fields of interlineated structures. The first 50 lines
form the blanking of the video picture. During these lines the vertical
flyback may take place and, for example, teletext information is to be
found in these lines. With the video information in the remaining 575
lines of a PAL video signal, a picture having the 4:3 aspect ratio may be
visualized on the picture screen. The picture screen of the currently
available television sets is then exactly filled. The frequency spectrum
of the lines in a PAL CVBS (chroma-video-blanking sync) signal are
represented in FIG. 2a1. The luminance signal Y.sub.1 in the video signal
is found in a frequency range from 0 to about 5 MHz. The chrominance
signal C is found in a frequency range from about 3.0 to 5 MHz. In this
frequency range the luminance and chrominance signals are frequency
interlaced. The chrominance signal is quadrature modulated with a
frequency of about 4.43 MHz (with a suppressed carrier). Furthermore, FIG.
2a2 show the signal content of a signal during one line period (1H) as a
function of time, with the sync S and the burst B. Thus, a picture having
a 4:3 aspect ratio may be displayed on the picture screen while covering
the entire screen.
Currently, video signal sources are known producing a video signal obtained
from a picture recording having a 16:9 aspect ratio. Such a
width-to-height ratio better fits in with the world of films and with the
properties of the human eye. Furthermore, there are picture display
devices having a picture screen with a 16:9 aspect ratio on which
pictures having a similar aspect ratio are displayed covering the entire
screen. 576 lines in the video picture are then available for this
purpose.
For displaying a picture having a 16:9 aspect ratio on a picture screen
having a 4:3 aspect ratio, 432 lines can be used. The picture screen is
then filled across its width. At the top and bottom of the picture screen,
however, black bands will then appear which are 72 lines in height. This
currently happens when some film formats are displayed on a television
picture screen.
A format for the video signal having pictures of a 16:9 aspect ratio is to
be proposed so that the reverse compatibility is ensured. This is to mean
that the video signal is to be such that the video signal is displayed on
a picture screen having a 16:9 aspect ratio and fully covers same and can
also be visualized on a picture screen having a 4:3 aspect ratio without
the loss of video information. This may be performed, for example, in the
manner described hereinbefore, that is to say, in the form of 432 lines in
a letterbox format with bands of 72 lines in height.
For this purpose a signal format is proposed known by the name of PAL-PLUS.
The structure of the PAL-PLUS video signal is as follows. A first field of
a number of blanking lines, 36 lines in the band referenced 1 in FIG. 1
(denoted "second" video lines), 216 lines of signal contents as those
already shown in FIG. 2a1 and 2a2 (referenced "first" video lines) and
again 36 second video lines in the band referenced 2 in FIG. 1. Then, a
second field also comprising a number of blanking lines, 36 second video
lines, 216 first video lines and again 36 second video lines. The two
fields together form the picture having a total of 625 lines.
The signal content in the second video lines is to be such that a standard
television set having a 4:3 picture screen displays this signal as a
picture in the part referenced 3 of the picture screen and having black
bands in the parts referenced 1 and 2 of the picture screen shown in FIG.
1. In addition, the signal contents in the second video lines are to be
such that, in combination with the signal contents in the 432 first video
lines, the contents may be used for displaying on a 16:9 picture screen a
picture which is 576 lines high and thus covers the entire screen.
FIG. 2b1 shows the frequency spectrum of the second video lines. The signal
in the second video lines has the shape of a luminance signal Y.sub.2
modulated with a frequency of about 4.43 MHz (with suppressed carrier),
and has a peak-to-peak amplitude of about 300 mV around the blanking
level. The frequency spectrum of the second luminance signal extends from
about 0.5 MHz to about 5 MHz. The second luminance signal may be AM or
quadrature modulated. FIG. 2b2 shows the signal plotted against time
during a video line time (1H). The second video lines furthermore include
a sync signal and a burst signal analogous to the first video lines.
In the following, FIG. 3 shows an exemplary embodiment of a recording
device according to the first option as stated hereinbefore, in which the
second luminance signal is recorded on the record carrier after an FM
modulation. FIG. 4 likewise shows an embodiment of a reproducing device
with which the video signal thus recorded on the record carrier can be
reproduced.
FIG. 3 shows an exemplary embodiment of a device for recording the PAL-PLUS
video signal on a magnetic record carrier. In this embodiment an
FM-modulated version of the second luminance signal Y.sub.2 is recorded in
a track on the record carrier. A PAL-PLUS video signal is applied to an
input of a separation unit 11 through an input terminal 10. The separation
unit 11 is arranged for deriving a (first) luminance signal from the
signal applied to its input and presenting this (first) luminance signal
at a first output 12 and for deriving a chrominance signal and presenting
same at a second output 13. This implies that if a video signal as shown
in FIG. 2a1 and 2a2 is applied to the input 14, the luminance signal
Y.sub.1 appears at the output 12 and the chrominance signal C at the
output 13.
If a recording device in the form of, for example, a VHS video tape
recorder is concerned, the separation unit 11 comprises, between the input
14 and the output 12, a low-pass filter having a cut-off frequency of
about 3.0 MHz and, between the input 14 and the output 13, a band-pass
filter having cut-off frequencies of 3.8 and 5 MHz. A luminance signal
Y.sub.1 then appears at the output 12 in a frequency range from 0-3.0 MHz
and a chrominance signal C at the output 13 in a frequency range from
3.8-5 MHz.
If a recording device in the form of an SVHS video tape recorder is
concerned, luminance and chrominance comb filters, respectively, are
inserted between the input 14 and the outputs 12 and 13. In that case a
first luminance signal will appear in a frequency range from 0 to about 5
MHz at the output 12 and a chrominance signal in the frequency range from
3.8-5 MHz at the output 13.
The device comprises a first signal path 15 including an FM modulator 16,
and a second signal path 17 including a mixer stage 18 and a low-pass
filter 25. The low-pass filter 25 is intended for removing undesired
mixing components from the output signal of the mixer stage 18. The output
of the signal path 15 is coupled to a first input 19 of a signal combining
unit 22. The output of the signal path 17 is coupled to a second input 20
of the signal combining unit 22. An output 21 of the signal combining unit
22 is coupled to an input 23 of writing means 24.
In the mixer stage 18 the chrominance signal C is mixed with a frequency of
about 5.06 MHz applied to an input 37 of the mixer stage 18. The mixing
frequency is derived in unit 39 in known fashion from the burst and the
sync in the video signal. After the mixing operation the chrominance
signal is then situated in a frequency range of .+-.500 kHz around a
carrier having a frequency of 627 kHz, cf. FIG. 2c. In the FM modulator 16
the first luminance signal Y.sub.1 is modulated to a frequency range above
1 MHz, cf. FIG. 2c. The arrow p denotes the frequency swing of the
carrier. For a VHS video tape recorder the frequency range of this
frequency swing is about 1 MHz wide and is situated between about 3.8 and
4.8 MHz. For an SVHS video tape recorder the frequency range is about 1.6
MHz wide and is situated between about 5.4 and 7.0 MHz.
In the signal combining unit 22 the two components are frequency-combined
to the signal as represented in FIG. 2c. In the writing means 24 this
signal is written in a helical scan-like fashion in tracks running side by
side on the record carrier in a direction at an angle to the longitudinal
direction of the record carrier.
The input 14 of the separation unit 11 is coupled to a first input 30 of
first controllable switching means 26 constituted by a two-way switch. The
output 12 of the unit 11 is coupled to a second input 31 of the switching
means 26. An output 32 of the switching means 26 is coupled to the input
of the signal path 15 via an automatic gain controller 27. The output 13
of the unit 11 is coupled to an input 33 of second controllable switching
means 28, an output 34 of which being coupled to the input of the signal
path 17 via an automatic gain controller 29. The second switching means 28
are also constituted by a two-way switch.
The third signal path for processing the second luminance signal is formed
in the arrangement shown in FIG. 3 by the signal path from the input
terminal 10 via the terminal 30 of switch 26, the terminal 32 of this
switch, the gain controller 27 and the FM modulator 16 to the input 19 of
the signal combining unit 22. The FM modulator 16 in this embodiment is
thus shared by the first and third signal paths.
In response to a control signal cs applied to the switch 26 through the
control signal input 35, during the presence of the burst and the second
luminance signal Y.sub.2 in the second lines in the PAL-PLUS video signal,
and during the presence of the burst in the first lines, the switch 26 is
in a state in which input 30 is connected to output 32. This achieves that
the second luminance signal in the second lines appears at the output 32
unmodified and is not processed in the luminance separation filter in the
separation unit 11 and that furthermore all burst are passed. During the
presence of the first luminance signal in the first lines, the switch 26
is in the state in which input 31 is coupled to output 32. The sync signal
in all the lines may be fed to the signal path 15 through either input 30
or input 31. The second luminance signal Y.sub.2 is then modulated in the
FM modulator 16 in identical manner to the first luminance signal Y.sub.1.
Thus, subsequent to FM modulation, the second luminance signal ends up in
the frequency range above about 1 MHz and may then be recorded in a track
on the record carrier by the unit 24. In response to the control signal cs
applied to the control signal input 36 of the switch 28, during the first
lines and during the occurrence of the bursts B in the second lines of the
video signal, the switch 28 is in the state in which input 33 is coupled
to output 34. During the presence of the second luminance signal in the
second lines the switch is opened. The reason for passing the bursts in
the second lines through the signal paths 15 and 17 is that the
phase-locked loops present remain locked during reproduction.
Though not represented in FIG. 3, a delay line may be inserted in the
branch from the input terminal 10 to the input 30 of switch 26 in order to
compensate for the delay differences developing between C and Y.sub.1, on
the one hand, and Y.sub.2, on the other, due to the processing of C and
Y.sub.1 in the separation unit 11.
It should be observed in this context that the exemplary embodiment shown
in FIG. 3 may be changed in the way that the input 31 of switch 26 is
coupled to the output 13 of unit 11, and that the output 32 of the switch
26 is coupled to the input of the AGC unit 29. This is shown, for example,
in the exemplary embodiment of FIG. 5 to be discussed hereinafter. In
addition, between the output of the AGC unit 29 and the input of the mixer
stage 18 a branch is inserted to a switch located before the FM modulator
16 in the first signal path, such as switch 90 in FIG. 5, so that the
second luminance signal can again be applied to the FM modulator 16.
FIG. 4 shows a reproducing device with which the PAL-PLUS video signal as
recorded with the device shown in FIG. 3 may be reproduced. The FM
demodulators in the first and third signal paths of the device shown in
FIG. 4 are shared, so that a single FM demodulator will suffice. The
device comprises reading means 40 for reading the information recorded on
the record carrier. An output 42 of the reading means is coupled to an
input 43 of a separation unit 41. The separation unit 41 is arranged for
deriving the first luminance signal Y.sub.1 from the signal read from the
record carrier, and for applying this luminance signal to a first output
44. The unit 41 thereto comprises a high-pass filter 46 having a cut-off
frequency of about 1 MHz. Because the second luminance signal Y.sub.2
after recording is situated in the same frequency range as the first
luminance signal, both the first and second luminance signals present in
the first and second lines respectively, in the video signal will appear
at the output 44. The separation unit 41 is further arranged for deriving
the chrominance signal C from the information that has been read out and
for applying this chrominance signal to an output 45. For this purpose,
the unit 41 comprises a low-pass filter 47 having a cut-off frequency of
about 1 MHz.
The output 44 of the unit 41 is coupled to an input of an FM demodulator
48. In the demodulator 48 the effect of the modulation in the FM modulator
16 in the recording device is eliminated. At the output 49 of the
demodulator 48 again the original first luminance signal Y.sub.1 appears
in the first lines and the second luminance signal Y.sub.2 in the second
lines. The output 49 is coupled to a first output terminal 50 of the
device to which the first luminance signal is applied for further
processing. The output 45 of the unit 41 is coupled to a second output
terminal 53 via an automatic gain controller 51 and a mixer stage 52. In
the mixer stage 52 the chrominance signal C is mixed with a frequency so
that again the original chrominance signal modulated on the fixed carrier
is obtained having a frequency of 4.43 MHz. After band-pass filtering in
the band-pass filter 69, in which disturbing modulation components are
filtered out, the chrominance signal is presented for further processing
at a second output terminal 53 through a comb filter 141. The comb filter
141 is intended for suppressing cross-talk from adjacent tracks.
The chrominance signal C as applied to an input 54 of the mixer stage 52 is
modulated on a carrier f.sub.dc which is no longer exactly equal to 627
kHz due to the time errors developed during the reading operation.
However, a chrominance signal modulated on a fixed carrier having a
frequency of 4.43 MHz is to be presented at the output terminal 53. For
this purpose, a mixing frequency of 4.43 MHz+f.sub.dc is applied to a
second input 55 of the mixer stage. This mixing frequency is obtained in
known fashion by means of a circuit 70 formed by a frequency oscillator
56, a phase comparator 59, a low-pass filter 60, a variable oscillator 61,
a mixer stage 58 and a band-pass filter 62. The oscillator 56 applies a
fixed frequency of 4.43 MHz to an input 57 of a mixer stage 58 and to an
input 63 of the phase comparator 59. The phase comparator compares the
4.43 MHz frequency of the oscillator 56 with the burst frequency presented
at an input 64. A difference signal generated by the phase comparator 59
is applied as a control signal to the control signal input 65 of the
oscillator 61 through the low-pass filter 60. In response to this control
signal the oscillator 61 generates at its output a frequency of f.sub.dc
which is applied to an input 66 of the mixer stage 58. A frequency of 4.43
MHz.+-.f.sub.dc then appears at the output 67 of the mixer stage 58. The
sum frequency is passed to the second input 55 of the mixer stage 52 by
the band-pass filter 62. By mixing the chrominance signal with this mixing
frequency, a frequency-shifted chrominance signal is obtained on the
desired fixed carrier of 4.43 MHz.
The suppressed carrier f.sub.dl of the second luminance signal Y.sub.2 in
the second lines of the video signal now no longer has the fixed value of
4.43 MHz, cf. the curve Y.sub.2 denoted 94 in FIG. 4, also due to the time
errors developed during the reading operation. The second luminance signal
thus needs a similar correction to the one applied to the chrominance
signal by means of the circuit 70 in conjunction with the mixer stage 52.
For this purpose, the output 49 of the FM demodulator 48 is coupled to a
circuit 71, that is to say, a first input 72 of a first mixer stage 73. A
frequency of 4.43 MHz+f.sub.dl is applied to a second input 74 of the
mixer stage 73. At the output 75 of the mixer stage 73 the second
luminance signal Y.sub.2 then appears modulated on a fixed carrier of 4.43
MHz. The frequency spectrum of the second luminance signal, however, is
frequency inverted as is shown by the curve 77 in FIG. 4. Being filtered
in the band-pass filter 76 in which disturbing modulation components are
filtered out, the signal is then applied to a first input 79 of a second
mixer stage 78. A second input 80 of this mixer stage 78 is supplied with
a frequency of 8.86 Mhz obtained in the multiplier 81 which has multiplied
the oscillation frequency of the oscillator 56 by two. Subsequent to
band-pass filtering in the band-pass filter 84, for filtering out
undesired mixing frequencies, the original second luminance signal Y.sub.2
then appears at the output 83 for further processing. In the phase
comparator 85 the frequency of the burst is compared with the fixed 4.43
MHz frequency of the oscillator 56. The output signal of this comparator
85 drives, through a low-pass filter 89, a variable oscillator 86, which
applies a frequency equal to f.sub.dl to the mixer stage 87. Once
undesired mixing frequency components have been filtered out in the
band-pass filter 88, the frequency of 4.43 MHz+f.sub.dl is presented at
the second input 74 of the mixer stage 73. The first signal path in the
device of FIG. 4 is thus formed by the path leading from the output 44 of
the separation unit 41, via the demodulator 48 to the output terminal 50.
The second signal path is formed by the path leading from the output 45,
via the gain controller 51 and the mixer stage 52 to the output terminal
53. The third signal path is formed by the path leading from the output 44
via the demodulator 48 and the mixer stages 73 and 78 to the output
terminal 83. Delay lines and switches may be coupled, as desired, to one
or more of the output terminals 50, 53 and 83, so as to correctly position
with time the two luminance signals and the one chrominance signal
relative to each other, to do away with undesired signals, and to combine
the signals again.
It should be observed in this respect that this reproducing device may
alternatively comprise only a single mixer stage in the third signal path,
that is, the mixer stage 73. By mixing the second luminance signal in this
mixer stage 73 with a frequency of, for example, f.sub.dl, this luminance
signal is demodulated direct to the baseband. The elements 78, 84, 87, 88
and 81 are then absent. The filter 76 then has a different filter
characteristic and the phase loop 71 is different in that the output of
the oscillator 86 has a direct coupling to the input 74 of the mixer stage
73 and the output of the FM demodulator 48 has a direct coupling to both
the input 72 of the mixer stage 73 and the one input of the phase
comparator 85 and in that the other input of phase comparator 85 is
coupled to the output of the oscillator 86.
From the above-discussed exemplary embodiments it has become apparent that
the mixer stage(s) located in the third signal paths of the recording and
reproducing system is (are both) located in the third signal path of the
reproducing device for processing the second luminance signal.
Hereinbelow, two exemplary embodiments (FIGS. 5 and 7) of recording devices
according to the second option as explained above will be discussed
hereinbelow, in which the second luminance signal is written on a record
carrier after the signal has been mixed to a different frequency range and
after an FM modulation. Then, two exemplary embodiments (FIGS. 6 and 8) of
a reproducing device will be discussed by means of which the video signal
thus recorded on the record carrier may be read out. In the exemplary
embodiments shown in FIGS. 5 and 7 the second luminance signal Y.sub.2 is
first converted to another frequency range, after which it is FM modulated
and recorded on the record carrier. The mixing frequency may be an
arbitrary frequency. A separate mixer stage may be used for this purpose,
cf. the mixer stage 130 in FIG. 7. Alternatively, the mixing frequency may
also be assumed to be equal to the 627 kHz carrier of the chrominance
signal C. In that case, the mixer stage 18 already available in the second
signal path cf. FIG. 5 will then preferably be used. However, also with a
shared mixer stage a mixing operation with a different frequency from 627
kHz in the mixer stage 18 is possible, that is, by changing the mixing
frequency supplied by unit 39 in the mixer stage 18.
The device shown in FIG. 5 comprises a switch 26 inserted between the
output at 13 of the separation unit 11 and the gain controller 29. The
branch from the second signal path 17 to a terminal 92 of a switch 90 in
the first signal path 15, used for transferring the second luminance
signal to the path 15, is situated behind the mixer stage 18. There is a
switch 28 after the mixer stage 18, that is, after the branch from the
second to the first signal path.
The operation of the switch 28 shown in FIG. 5 is equal to the operation of
the switch 28 shown in FIG. 3.
In response to a control signal applied to the input 36', the switch 90 is
in the state in which the input 92 is connected to the output 93 during
the presence of the second luminance signal in the second lines and during
the bursts in the first and second lines, and the switch is in the other
state for the remaining period of time.
In response to the control signal applied to the input 35, the switch 26 is
in the state in which input 30 is connected to output 32 during the
presence of the second luminance signal in the second lines. During the
absence of the chrominance signal the switch is in the other state. The
bursts in all the lines are preferably passed to the mixer stage 18
through the switch input 31. The sync signals in all the lines must not be
applied to the second input 20 of the signal combining unit 22. Either
switch 26 or switch 28 may be used for achieving this.
The second luminance signal Y.sub.2 in the second lines is frequency
shifted and inverted in the mixer stage 18. The suppressed carrier is now
situated at a specific frequency, for example, 627 kHz. The signal thus
obtained is applied to the FM modulator 16 through the low-pass filter 25
in which undesired mixing components are filtered out. The second
luminance signal thus obtained is FM modulated and recorded on the record
carrier. It should be observed in this respect that where the second
luminance signal is mixed with a different frequency from the chrominance
signal mixing frequency, the bursts in all the lines are mixed with the
mixing frequency with which the chrominance signal is mixed.
In this exemplary embodiment the third signal path is formed by the path
leading from the input terminal 10, through the terminals 30 and 32 of the
switch 26, the mixer stage 18, the low-pass filter 25a, the terminals 92
and 93 of the switch 90 and the modulator 16 to the input 19 of the signal
combining unit 22.
FIG. 6 shows a reproducing device with which the information recorded on
the record carrier by means of the device shown in FIG. 5 may be
reproduced. The device presents great similarity to the one shown in FIG.
4. The signal processing of the first luminance signal Y.sub.1 and a
chrominance signal C is identical. At the output of the demodulator the
second luminance signal Y.sub.2 in the second lines has a frequency
spectrum as shown by the curve 120 in FIG. 6. The second luminance signal
is situated on a carrier of, for example, about 627 kHz. Thus, the only
operation that needs doing is a mixing in the mixer stage 73 to a fixed
carrier frequency of 4.43 MHz. Such a mixing operation is completely
identical with the mixing operation performed with the chrominance signal
C in the circuit 70. For this purpose, a mixing frequency of 4.43
MHZ+f.sub.dl is applied to the second input 74 of the mixer stage 73.
Because the frequency spectrum of the second luminance signal in the mixer
stage 18 of the device shown in FIG. 5 is inverted, the frequency spectrum
of the second luminance signal Y.sub.2 to be inverted back to its original
shape after the mixing operation in the mixer stage 73.
FIG. 7 shows a recording device to be used in lieu of the device shown in
FIG. 5 for recording a PAL-PLUS video signal. Also in this case the second
luminance signal Y.sub.2 is first converted to a different carrier
frequency, then FM modulated, after which it us recorded on the record
carrier. For the conversion to the different carrier frequency use is made
of a separate mixer stage 130 inserted between the output of the gain
controller 27 and the input 107 of controllable switching means 105',
constituted by a switch. The reason for using a separate mixer stage for
the second luminance signal is that the chroma carrier used in the mixer
stage 18 for mixing the chrominance signal, for example, for each
consecutive line in the video signal is to be phase shifted through
90.degree.. However, this is not necessary for mixing the second luminance
signal.
The mixing frequency with which the second luminance signal is mixed in the
mixer stage 130, and which is produced by a source 131, may again be the
same as the mixing frequency of mixer stage 18. A different mixing
frequency could also be selected as required.
The operation of the switch 26 in response to the control signal is again
the same as that discussed with respect to FIG. 3.
The controllable switch 105' operates in such a way that the input 107 is
connected, in response to the control signal, to the output 108 during the
presence of the second luminance signal in the second lines, and during
the presence of the bursts in the first and second lines in the video
signal. For the remaining period of time the switch is in another state.
The device shown in FIG. 6 may again be used as a reproducing device.
If the second luminance signal and the burst have different modulations
during recording, oscillator 86 in FIG. 6 has a different frequency from
oscillator 61. If the second luminance signal and the burst are mixed with
the same frequency during recording, the frequencies of the oscillators 86
and 61 are equal.
If the second luminance signal Y.sub.2 in the recording device shown in
FIG. 5 or 7 is mixed with the same frequency as used for mixing the
chrominance signal, or with a frequency derived therefrom, a
simplification of the reproducing device shown in FIG. 6 is possible. This
simplification is shown in the reproducing device of FIG. 8. The device
comprises first controllable switching means 150 constituted by a switch,
having a first input 151 coupled to the output of the FM demodulator 48,
and a second input 152 coupled to the output of the AGC unit 51, and an
output 153 coupled to the input 54 of the mixer stage 52.
In response to a control signal applied to the control signal input 159 of
the switch 150, this switch is in the state in which input 151 is
connected to output 153 during the presence of the second luminance signal
in the second lines in the video signal. During the presence of the
chrominance signal in the first lines, the switch is in the state shown in
the drawing Figure. During the bursts and sync signals in the first and
second lines, the switch 150 is preferably in the bottom state.
The exemplary embodiments discussed so far with respect to the FIGS. 5, 6,
7 and 8 have clarified that from the two mixer stages located in the third
signal paths of the recording and reproducing system, for processing the
second luminance signal, one mixer stage is located in the third signal
path of the recording device, and one mixer stage is located in the third
signal path of the reproducing device.
It should be further be noted that the second luminance signal Y.sub.2 in
the embodiments of FIGS. 5 and 7, is preferably additionally processed in
the sense that a DC voltage V.sub.DC is added to the second luminance
signal, see FIG. 19. The reason is that otherwise large signal components
in the second luminance signal could lead to a detection of false syncs in
the sync separator, which is present in the recording and the reproducing
device.
The adding of a DC voltage to the second luminance signal can be realized
by means of a signal adding circuit (not shown) that can be included in
one of the two input paths to the mixer stages 18 and 130 in FIG. 5 or 7,
respectively, or in the output path of said mixer stages.
The DC voltage V.sub.DC should have such a value that the lowest signal
values of Y.sub.2 are larger than the black level. V.sub.DC is for
instance 350 mV, which is a DC level of 50% (half grey).
At the reproduction side, that is in the embodiments of FIGS. 6 and 8, the
inverse signal processing should be carried out. That means that the same
DC voltage V.sub.DC should be subtracted from the second luminance signal
Y.sub.2. This can be realised by including a signal subtracting circuit
(not shown) in one of the two input paths of the mixer stages 73 and 52 in
FIG. 6 or 8, respectively, or in the output path of said mixer stages.
It should be noted that the adding and subtracting of the DC voltage
to/from the second luminance signal Y.sub.2 should only be applied to the
second luminance signal Y.sub.2 as it is present in the second lines. The
adding and subtraction circuits are inhibited during the first lines of
the video signal.
A problem that might occur during reproduction is, that the level for half
grey is not known any more. This could mean that the inverse signal
processing by means of the subtracting circuit could lead to a regenerated
second luminance signal having an erroneous DC level. In order to preclude
such a situation, level information concerning the exact level of half
grey could be transmitted together with the video signal. Upon
reproduction this level information can be detected and used to bring the
second luminance signal reproduced at its correct DC level.
An other possibility is, not to bring the second luminance signal back to
its original level, but to apply the level information together with the
reproduced video signal to a PAL-PLUS decoder, in which the second
luminance signal is brought back to its original level in the PAL-PLUS
decoding step.
In FIG. 9 is shown an exemplary embodiment of a recording device according
to the third option as stated above, in which the second luminance signal
is also mixed with a certain frequency after which the second luminance
signal mixed to a different frequency range is recorded direct. This will
be followed by an exemplary embodiment (in FIG. 10) of a reproducing
device with which the video signal thus recorded on the record carrier may
be read out.
FIG. 9 shows the recording device in which the second luminance signal
Y.sub.2 is mixed in mixer stage 18 and then recorded on the record carrier
in a wide-band frequency range. The second luminance signal Y.sub.2 is
thus recorded with a frequency spectrum as shown in FIG. 2d on the record
carrier during the second video lines. A carrier frequency corresponding
to black (cf. FIG. 2d) then leaves the FM modulator 16, so that the whole
frequency range of the storage medium may be used for recording the second
luminance signal Y.sub.2. During the first video lines the signal having
the characteristic of FIG. 2c is recorded. The switching means 26 are
included in the circuit leading from the second output 13 of unit 11 to
the second signal path 17. The operation of the switch 26 is again equal
to that of this switch in the device shown in FIG. 5. The device further
includes switching means 171 in the form of a controllable switch for
switching off the filtering operation of the low-pass filter 25. This
switch bridges the filter 25. The operation of the switch 171 is as
follows. Switch 171 is closed in response to the control signal at a
control signal input 172 during the presence of the second luminance
signal, open during the presence of the chrominance signal and preferably
also open when the sync signals and bursts occur in all the lines. This
achieves that the wide-band signal for the second luminance signal Y.sub.2
as shown in FIG. 2d which wide-band signal is obtained after the mixing
operation in the mixer stage 18, may be applied direct to the recording
unit 24 without passing through the low-pass filter 25.
FIG. 10 shows an exemplary embodiment of a reproducing device for reading
information recorded by the device shown in FIG. 9 from the record
carrier. The separation unit 41 in this structure further includes
bridging means 180 which may bridge the low-pass filter 47. These bridging
means 180 are constituted by a controllable switch which operates in
similar fashion to the switch 171 in FIG. 9 in response to the control
signal applied to the control signal input 183. The wide-band second
luminance signal Y.sub.2 in these second lines may reach the mixer stage
52 without passing through the filter 47.
In the exemplary embodiments shown in the FIGS. 9 and 10 and discussed
hereinbefore it has become apparent that from the two mixer stages
included in the third signal paths of the recording and reproducing
system, for the processing of the second luminance signal there is one
mixer stage in the third signal path of the recording device and one mixer
stage in the third signal path of the reproducing device.
It should further be observed that similar to the exemplary embodiments
shown in FIGS. 5 and 7, also the exemplary embodiment shown in FIG. 9 may
comprise two mixer stages or a switching mixer stage to be used for mixing
the second luminance signal with another mixing frequency. A similar line
of thought also holds for the reproducing device shown in FIG. 10.
With the converter means shown in FIGS. 11 and 12 it is possible to record
a PAL-PLUS video signal on a standard (S)VHS tape recorder and to derive
the second luminance signal from the signal reproduced by the video tape
recorder. For recording the converter means shown in FIG. 11 is to be
connected to the CVBS input of the (S)VHS video tape recorder. For
reproduction the converter means shown in FIG. 12 is to be connected to
the CVBS output of the (S)VHS video tape recorder. The PAL-PLUS video
signal is presented at the input terminal 200 of the converter means shown
in FIG. 11. The terminal 200 is coupled to a first input 201 of
controllable switching means 202 via a delay line 209, and to a second
input 203 of the switching means 202 constituted by a switch via a gain
controller 206, a mixer stage 207 and a low-pass filter 208. The output
204 of the switch 202 is coupled to the output terminal 210 of the
converter means. In response to a control signal applied to the control
signal input 205, the switch 202 is in the state in which the input 203 is
connected to the output 204 during the presence of the second luminance
signal in the second lines in the video signal. In the absence thereof,
the switch is in the other state. This means that the chroma bursts in all
the lines are applied to the output 210 through the path 211. During the
second video lines the second luminance signal is passed through the
signal path 212. A mixing is performed with a frequency, for example,
equal to 4.43 MHz, in the mixer stage 207. This mixing operation causes
the second luminance signal to be mirror inverted and frequency shifted.
Subsequent to low-pass filtering in the filter 208, during which undesired
mixing components are filtered out, the thus obtained signal is applied to
the input 203 of the switch 202. The signal at the output terminal 210 is
situated in such a frequency range that it can be recorded by a VHS or
SVHS video tape recorder.
During reproduction, this video signal is again read out and applied to the
input terminal 220 of the converter means shown in FIG. 12. The terminal
220 is coupled to a first input 222 of controllable switching means 223
through a delay line 221, and to a second input 226 of the switching means
223 constituted by a switch through a mixer stage 224 and a band-pass
filter 225. The output 227 of the switch 223 is coupled to the output
terminal 228 of the converter means. In response to a control signal
applied to the control signal input 229 the switch 223 similar to the
switch 202 has the bottom state only during the presence of the second
luminance signal. During the first video lines the first luminance signal
and the chrominance signal are passed through the signal path 230
unmodified. During the second video lines the second luminance signal is
passed through the signal path 231. A mixing is performed in mixer stage
224 with a frequency, for example, equal to 4.43 MHz. As a result of the
mixing in the mixer stage 224, the second luminance signal Y.sub.2 is
again reset to the original frequency range shown in FIGS. 2b and 2b2.
Subsequent to band-pass filtering in the band-pass filter 225, in which
undesired mixing components are filtered out, the thus obtained signal is
applied to the terminal 226 of the switch 223. The signal at the output
terminal 228 is again the PAL-PLUS video signal which may be applied to
the CVBS input of the television set.
The converter means shown in FIGS. 11 and 12 are used for realizing the
recording and reproducing system according to the second option, in which
the second luminance signal is first mixed and then FM modulated prior to
being recorded. The FM modulation is effected in the VHS video tape
recorder.
FIG. 13 shows an extension of the converter means shown in FIG. 11 in which
the converter means furthermore includes a separation unit 235, which has
an input 236 coupled to the terminal 200, an output 237 coupled to the
signal path 211 and an output 238 coupled to a signal path 244. The signal
path 244 furthermore includes a delay line 239 and a controllable switch
240 and is coupled to an output terminal 243. The outputs 210 and 243 may
be applied to the Y or C input, respectively, of an SVHS video tape
recorder. The separation unit 235 derives the first luminance signal
Y.sub.1 and the chrominance signal C from the input signal and applies
these luminance and chrominance signals to the output 237 or 238,
respectively. The first luminance signal is applied to the terminal 210
over the signal path 211 in a fashion described with reference to FIG. 11.
The second luminance signal is applied to the terminal 210 through the
signal path 212 which has a direct link to the terminal 200. The
processing in the signal path 212 of the luminance signal Y.sub.2 is equal
to the processing described with reference to FIG. 11. The switch 202
operates in such a way that during the absence of Y.sub.2, and preferably
also during the presence of the bursts in the first and second lines of
the video signal, the terminals 203 and 204 are connected to each other.
The chrominance signal is applied to the terminal 243 over the signal path
244. In response to the control signal applied to the control signal input
245, during the presence of the chrominance signal in the first lines and
during the presence of the bursts in the first and second lines of the
video signal, the switch 240 is in the state in which the input 241 is
connected to the output 242. During the presence of Y.sub.2 in the second
lines, the switch 240 is in a state in which the input 246 is connected to
the output 242.
The signals Y and C at the output terminals 210 and 243 are applied to the
Y and C inputs of an SVHS video tape recorder and are recorded by this
video tape recorder.
When reproduced, this video signal is again read out and presented to the
input terminals 220 and 250 of the converter means shown in FIG. 14. The
first and second luminance signals are presented to the terminal 220 and
the chrominance signal to the terminal 250. The converter means shown in
FIG. 14 comprises a signal path 260 from the input terminal 250 to an
output terminal 257. In this signal path there is a delay line 251 and
controllable switching means 252. The second luminance signal is fed to
the input 254 of the switch 252 after the signal has been mixed. The
mixing frequency of, for example, 4.43 MHz is derived from the chroma
burst in the signal path 260, while making use of the burst in the signal
path 231 as required. In response to the control signal, during the
presence of Y.sub.2 in the second lines, the switch 252 is in the state in
which the input 254 is connected to the output 256, so that the second
luminance signal is presented at the output terminal 257 during the second
video lines. During the remaining period of time the switch 252 is in the
state in which the input 255 is connected to the output 256. The
chrominance signal and the bursts in the first and second lines are then
presented at the output 257. In the first signal path 230 there is still
the controllable switch 223 which, during the presence of Y.sub.1 in the
first lines and the sync signals in the first and second lines, is in a
state in which the input 222 is connected to the output 227 and, during
the presence of Y.sub.2 and preferably the bursts in the first and second
lines, is in another state. The signals at the output terminals 228 and
257 may be fed to the Y and C inputs, respectively, of a television set.
FIG. 15 shows a different converter means which may be used in lieu of the
converter means shown in FIG. 14. The difference is to be found in the
fact that the output of the filter 225 is now coupled to the input 226 of
the switch 223. The switch 223, like the switch 223 in FIG. 14, is
similarly responsive to the control signals fed to the control signal
input 229.
Preferably the converter means of FIGS. 11 and 13 include a DC voltage
adding circuit so as to add a DC voltage V.sub.DC to the second luminance
signal, as explained with reference to FIGS. 5, 7 and 19. Also the
converter means of FIGS. 12, 14 and 15 preferably include a DC voltage
subtracting circuit so as to bring the second luminance signal back to its
original level.
Some of the converter means of FIGS. 11 to 15 can also be used if the
recording of a ED video signal, such as the PAL-PLUS video signal on a
digital video recorder is contemplated.
An embodiment of a digital video recorder is shown in FIG. 16. Recording
and subsequent reproduction of an SD video signal, such as a PAL signal is
as follows.
A PAL video signal, having the frequency characteristic according to FIGS.
2a1 and 2a2, is applied to an input terminal 300 of the video recorder and
is fed to a signal separator 301 in which the video signal is splitted
into its (first) luminance signal Y.sub.1 and its chrominance signal C.
The chrominance signal C is applied to a further signal separator 302, in
which the chrominance signal C is mixed, so that it is down converted in
frequency to a baseband signal. Further the down converted chrominance
signal is splitted into its U- and V-signal components. FIG. 16
schematically shows the frequency characteristic of the U- and
V-components. After A/D conversion in an A/D converter 303, the
chrominance signal Y.sub.1 and the U- and V-components are applied in a
DCT circuit 304, in which a discrete cosine transform is carried out
separately on each of the three signals.
A data reduction is carried out separately on each of the three DCT
transformed signals in a data reduction stage 305. After carrying out a
channel coding step separately on each of the three signals in a channel
coding stage 306, the three signals are recorded on the magnetic record
carrier by writing means 307.
Reproduction of the signals is carried out in a way inverse to the signal
treatment during recording. After read-out of the signal in reading means
308, the digital signal read out is detected in detector 309 and the
digital signal components Y.sub.1, U and V are applied to a decoder 310 in
which the original digital Y.sub.1, U and V signal components are
regenerated. After D/A conversion in the D/A converter 311, the three
signal components are combined in signal combination units 312 and 313 so
as to obtain the original PAL signal at the output 314.
It should be noted that the two splitter stages 301 and 302 could have been
combined so as to obtain the Y.sub.1, U- and V-components in one signal
splitting step, and that the two combination units 312 and 313 could have
been combined so as to obtain the PAL signal in one combining step from
the Y.sub.1, U and V components.
In order to make the digital video signal described above suitable for
recording an ED video signal, such as a PAL-PLUS video signal, the
following steps should be taken.
A possibility is to leave the digital video recorder unmodified and add
converter means, such as the converter means as per FIG. 17, such that the
output 210 of the converter means of FIG. 17 is connected to the input 300
of the digital video recorder, and to connect the converter means of FIG.
18 with its input 220 to the output 314 of the digital video recorder. The
PAL-PLUS video signal should be applied to the input 200 of the converter
means of FIG. 17, and a regenerated PAL-PLUS video signal will be
available at the output 228 of the converter means of FIG. 18. The
converter means of the FIG. 17 and 18 show a larger resemblance with the
converter means of FIG. 11 and 12, respectively, with the exception that a
signal adding circuit 320 for adding a DC voltage V.sub.DC to the second
chrominance signal, is inserted between the output of the mixer stage 207
and the input 203 of the switching means 202 in the converter means of
FIG. 17, and a signal subtracting circuit 322 for subtracting a DV voltage
V.sub.DC from the second luminance signal, is inserted between the input
220 and the input of the mixer stage 224 of the converter means of FIG.
18.
Applying the PAL-PLUS video signal directly to the input 300 of the digital
video recorder of FIG. 16 means that a DCT transformation is carried out
in the DCT circuit 304 on the second luminance signal. If the second
luminance signal is not down converted in frequency, this signal includes
a large high frequency contents. A DCT transformation carried out on such
a signal results in only a small data reduction to be obtained. For that
reason, the second luminance signal should be mixed so as to convert the
second luminance signal in frequency to baseband. This is realized by
means of the mixer stage 207 in the converter of FIG. 17, in which the
second luminance signal is mixed with a mixing frequency of 4.43 MHz. DCT
transformation carried out on the down converted second luminance signal
results in a much larger amount of data reduction.
A second problem that can occur when applying the PAL-PLUS video signal
directly to the digital video recorder of FIG. 16 is, that the operating
range of the A/D converter 303 for A/D converting the luminance signal
(the first luminance signal as well as the second luminance signal) is not
suitable for A/D converting the second luminance signal.
This is well understood when comparing the time signals in FIGS. 2a1, 2a2,
2b1 2b2. The operating range of the A/D converter is such that the first
luminance signal as it is included in the time signal of FIGS. 2a1 and 2a2
is well A/D converted. In order to bring the second luminance signal in
the said operating range of the A/D converter a DC voltage V.sub.DC is
added to the second luminance signal, so as to obtain a signal as shown in
FIG. 19.
V.sub.DC equals such a value that the active part of the signal lies well
within the linear range of the A/D converter. V.sub.DC can equal the value
of 350 mV given before (the half grey level).
During reproduction, the same DC voltage V.sub.DC is subtracted in signal
subtracting circuit 322 from the signal included in the second lines so as
to obtain the original down converted second luminance signal, see FIG.
18. After mixing the down converted second luminance signal in the mixer
stage 224 with a frequency of 4.43 MHz, the original second luminance
signal is obtained.
Preferably, amplifiers 321 and 323 are inserted in the converter means of
FIGS. 17 and 18, respectively. The amplifier 321 can be a compressor and
is adapted to compress the signal applied to its input prior to A/D
conversion. This realizes an optimal representation of the second
luminance signal in the digital domain as regards signal-to-noise ratio.
The amplifier 323 is an expander, which realizes a signal processing to
the second luminance signal after D/A conversion which is inverse to the
signal processing carried out by the amplifier 321.
In a digital recording and reproduction system, a level shift for the half
grey level, as has been explained for the analog recording and
reproduction system, does not occur, so that there is no need to transfer
information concerning the exact value of the half grey level together
with the video information to the reproducing side.
FIG. 20 shows a converter means that can be used as an input circuit in the
digital video recorder of FIG. 16. More specifically, the converter means
of FIG. 20 can replace the splitter circuit 301 in FIG. 16. In an
equivalent way, the converter means of FIG. 21 can be incorporated in the
signal combining circuit 313 in FIG. 16. The signal processing carried out
on the second luminance signal in the converter means of FIGS. 20 and 21
is identical to the signal processing as carried out on the second
luminance signal in the converter means of FIGS. 17 and 18, respectively.
Further, the functioning of the converter means of FIGS. 20 and 21 as to
the signal processing carried out on the first luminance signal and the
chrominance signal is identical to that of the converter means of FIGS. 13
and 15, respectively.
It should be noted that, where in the previous embodiments switching means
occur for switching between two input signals so as to bring one of the
input signals to their outputs, also other kinds of signal combination
units than switches can be used as means to bring the two input signals in
their correct form and at the correct moment to their outputs.
Further, it should be noted that the converter means shown in the FIGS. 11
to 15, 17, 18, 20 and 21 can be in the form of separate units or can be
incorporated partly or wholly in a video recorder. If the converter means
are in the form of separate units, it is well possible to use the
converter means in other kinds of transmission systems than video
recorders, so as to convert the ED video signal before transmission and to
reconvert the video signal received after transmission so as to regenerate
the ED video signal.
A further remark is that the signal adding circuits 320 in the converter
means of FIGS. 17 and 20 are inserted in the signal path of the second
luminance signal, preferably after the mixer stage 207. It is however also
possible to insert the signal adding circuits 320 before the inputs of the
mixer stage 207. The signal subtracting circuits 322 in the converter
means of FIGS. 18 and 21 are inserted in the signal path of the second
luminance signal, preferably before the mixer stage 224. It is however
possible to insert the subtracting circuits 322 behind the mixer stage 224
or before the other input of the mixer stage 224.
With respect to the control signals necessary for controlling the switches
in the various exemplary embodiments, it may be stated that these control
signals may be derived in a simple manner in a control signal generator
from the vertical and horizontal sync signals in the video signal,
furthermore, counters being necessary for discriminating between the first
and second video lines in a video image. On the basis hereof it is simply
possible for the expert to derive switching signals so that the switches
operate in the fashion described with reference to the embodiments.
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